In recent years, as the electronic circuits are disposed in a high density, the requirement for the miniaturization of electronic component is increasing. Besides, as the laminated ceramic capacitor is quickly developed to have a small size and a large capacity, more applications are provided and various properties are required.
For example, in a capacitor having a rated voltage higher than 100 V for mid-high voltage application, a high electrostatic capacity is required under an electric field with a high intensity, wherein the mentioned capacitor for mid-high voltage application is used in an ECM (engine electric computer module), a fuel injecting device, an electronic controlled throttle, an inverter, a converter, an HID head lamp unit, a battery controlling unit for a hybrid engine, a digital still camera or the like.
However, the conventional dielectric ceramic composition is designed on the premise of being used under a direct voltage having a low electric field intensity of, for example, about 1 V/μm, so the used laminated ceramic capacitor is developed to be thinner and thinner. If such a ceramic capacitor is used under an electric field with a high intensity, a problem rises that the variation rate of the electrostatic capacity relative to the applied direct current electric field (hereinafter referred to as the variation rate of DC bias) becomes larger.
If the variation rate of DC bias is large, the effective capacity in the laminated ceramic capacitor will decrease, and the required electrostatic capacity in the designing stage will not be satisfied. Thus, there might be problems such as the behavior of the electronic device using the laminated ceramic capacitor becomes unstable or even the electronic device does not work anymore.
Therefore, with respect to a capacitor to be used in a high electric field, the variation rate of DC bias should be small. Besides, a dielectric ceramic composition is expected to be used which has a high permittivity when a high electric field is applied. In addition, the “high electric constant” described here refers to, for instance, an intensity of 5 V/μm for the electric field, and a high permittivity refers to, for example, 1000.
In order to solve the technical problem mentioned above, the following Patent Document 1 has disclosed a dielectric ceramic composition with the following characteristics. In particular, it contains a main component and a subcomponent, wherein the main component consists of barium titanate having 0.02 wt % or less of oxide of alkali metal(s), at least one selected from the group consisting of europium oxide, gadolinium oxide, terbium oxide, dysprosium oxide, holmium oxide, erbium oxide, thulium oxide and ytterbium oxide, barium zirconate, magnesium oxide, manganese oxide and can be represented by the formula of (BaO)mTiO2+αR2O3+βBaZrO3+γMgO+gMnO (in the formula, R2O3 is at least one selected from the group consisting of Eu2O3, Gd2O3, Tb2O3, Dy2O3, HO2O3, Er2O3, Tm2O3 and Yb2O3, α, β, γ and g represent the molar ratios, and 0.001≦α≦0.06, 0.005≦β≦0.06, 0.001<γ≦0.12, 0.001<g≦0.12, γ+g≦0.13, and 1.000<m≦1.035), and the subcomponent is silicone oxide contained in an amount of 0.2 to 5.0 mol calculated in terms of SiO2 relative to 100 mol of the main component. However, even though the ceramic capacitor using the dielectric ceramic composition shown in Patent Document 1 as the dielectric material has a relatively high relative permittivity of about 1500, it has a high variation rate of DC bias as large as −45% or less under an electric field of 5 V/μm. In this respect, the DC bias related properties are expected to be further improved.
In addition, Patent Document 2 has disclosed a dielectric ceramic composition as follows. In particular, it is a dielectric ceramic which contains Ca, Sr, Mg, Mn and rare earth element(s), and the dielectric ceramic contains main grains which are formed by dissolving at least part of the Ca, Sr, Mg, Mn and the rare earth element(s) as solid solute in perovskite-type grains of barium titanate (BCT-type grains) in which part of A site is replaced by the Ca. In the dielectric ceramic, the amount of Al is 0.01 mass % or less when calculated in terms of oxides. The main grains have a higher concentration of Ca at the grain surface than that at the grain center and are of a core-shell structure with Sr, Mg, Mn and the rare earth element(s) unevenly distributed at the grain surface. Further, the grains have an average grain size of 0.1 to 0.5 μm.
However, although the BCT-type dielectric ceramic composition as shown in Patent Document 2 has a large relative permittivity of 2500 or more, it has a large variation rate of DC bias of −70% or less under an electric field of 5 V/μm. Thus, the DC bias related properties cannot be said to be good.